The present invention relates to a method and an apparatus for stabilizing a vehicle in the presence of a tilt tendency.
Methods and apparatuses for stabilizing a vehicle in the presence of a tilt tendency of many variations are conventional.
German Patent 32 22 149 describes a method and a device for preventing lateral tilting of a vehicle. The vehicle in this case is a straddle loader. The apparatus contains a measurement device for calculating the height of the overall center of gravity of the vehicle with the load. It furthermore contains a device for calculating the static stability of the vehicle, as a critical reference value, from the quotient of the vehicle track and twice the height of the overall center of gravity. The apparatus also contains a device for calculating the dynamic instability from the quotient of the vehicle speed squared and the product of the curve radius (calculated from the respective control angle) times the acceleration of gravity. If the dynamic instability exceeds the reference value, the speed of the vehicle is reduced. This is done by activating the vehicle brakes and the corresponding actuation of the engine clutch.
PCT Application No. 97/28017 describes a vehicle dynamic control method and a corresponding apparatus for commercial vehicles that are equipped with an ABS system. With this method and apparatus, a decrease in the tilt stability of the vehicle while traveling through a curve is determined on the basis of the utilization of an ABS control intervention. For this purpose, a determination is made as to whether the transverse acceleration of the vehicle exceeds a limit value defined for it. If the transverse acceleration exceeds this limit value, a braking intervention, which is smaller relative to the maximum possible braking force, is initiated. Monitoring then takes place, by measuring the power supply at the plug connector of the tractor or at the ABS valve, to determine whether the ABS system responds. If a response is detected, an alarm signal is triggered and/or a control intervention that increases tilt stability, for example a braking event, is performed.
German Patent No. 196 32 943 describes a method for operating a motor vehicle having a braking system with which wheels on the same axle can be braked independently of one another. With the method, vehicle-stabilizing braking interventions are performed automatically by way of the braking system. At least one instantaneous value for a vehicle-dynamics parameter indicative of the vehicle tilt tendency about the longitudinal vehicle axis is continuously compared to an associated tilt-prevention threshold value. As soon as one of the instantaneous values exceeds the associated threshold value, the wheels on the outside of the curve are braked for tilt-prevention purposes.
German Patent No. 43 42 732 describes equipping a tanker vehicle with sensors to monitor the tilt susceptibility of the tanker vehicle. The sensors provided detect wheel loads. The sensors are connected to an analysis circuit. If a potential tilting hazard is detected, then the road speed of the tanker vehicle is reduced by way of the drive system and/or braking system.
The analysis of a variable describing the change in slip and/or a variable describing the diameter or the radius of a wheel is not described by any of the above-referenced patents. In addition, the performance of a controlled braking intervention on the front wheel on the outside of the curve is not described in any of these documents.
An object of the present invention is to provide a method for stabilizing a vehicle in the presence of a tilt tendency with which a tipover of the vehicle is prevented; which, in order to determine the tilt tendency, uses variables in alternative to the wheel loads; and which, when a tilt tendency exists, makes possible an alternative intervention on the braking system in order to stabilize the vehicle.
The method stabilizes a vehicle in the presence of a tilt tendency. For this purpose, for at least one wheel, a variable quantitatively describing the wheel behavior of the corresponding wheel is determined. A determination is also made, at least as a function of the variable quantitatively describing the wheel behavior that was determined for the at least one wheel, as to whether a tendency to tilt about a vehicle axis oriented in the longitudinal direction of the vehicle exists for the vehicle. If a tilt tendency exists, then at least stabilizing braking interventions on at least one wheel of the vehicle are preformed.
According to the present invention, for at least one wheel, a variable describing the slip and/or a variable describing the diameter or the radius of the respective wheel are determined as the variable that quantitatively describes the wheel behavior. As a function of a variable that describes the change in the slip of the respective wheel or the variable describing the diameter or the radius of the respective wheel, a determination is made as to whether a tilt tendency about a vehicle axis oriented in the longitudinal direction of the vehicle exists for the vehicle. With this method, a tipover of the vehicle is prevented.
The use of the two aforementioned variables has the following advantage: These variables are each directly correlated with the tire behavior. Since a tipover of the vehicle initially becomes apparent in the tire behavior, evaluating these variables in terms of the time at which a tipover tendency is detected yields an advantage in terms of time.
Note that when the term xe2x80x9ctilt tendency of the vehiclexe2x80x9d is used hereinafter, it means the xe2x80x9ctilt tendency of the vehicle about a vehicle axis oriented in the longitudinal direction of the vehicle.xe2x80x9d The term xe2x80x9ca vehicle axis oriented in the longitudinal direction of the vehiclexe2x80x9d is to be understood as follows: In the case of the vehicle axis about which a tilt tendency of the vehicle occurs, it can be the actual longitudinal vehicle axis. It may also be a vehicle axis that is rotated through a certain angle with respect to the actual longitudinal vehicle axis. It is immaterial in this context whether the rotated vehicle axis passes through the center of gravity of the vehicle. The instance of the rotated vehicle axis is also intended to allow for an orientation of the vehicle axis in which the vehicle axis corresponds either to a diagonal axis of the vehicle or an axis parallel thereto.
Advantageously, a variable dependent on the wheel load acting on the respective wheel is determined for the at least one wheel as the variable quantitatively describing the wheel behavior of the respective wheel.
It is advantageous to determine for the at least one wheel, as the variable quantitatively describing the behavior of the respective wheel, a variable that describes the diameter or the radius of the respective wheel. This variable is determined at least as a function of a variable describing the wheel rotation speed of the corresponding wheel, a variable describing the vehicle speed, a variable representing the transverse dynamics of the vehicle, and a variable describing the geometry of the vehicle. For this, what is advantageously determined as the variable representing the transverse dynamics of the vehicle is a variable describing the yaw rate of the vehicle and/or a variable describing the transverse acceleration of the vehicle; and the variable describing the vehicle speed is determined at least as a function of variables, determined for the wheels, which describe the wheel rotation speeds.
The following procedure is advantageously useful for detecting the tilt tendency of a vehicle: For at least one wheel, a variable describing the wheel rotation speed is determined. In addition, at least one variable representing the transverse dynamics of the vehicle is determined. At least as a function of one of the variables representing the transverse dynamics of the vehicle, braking torques and/or drive torques are briefly generated and/or modified at at least one wheel. While the braking torques and/or drive torques are being briefly generated and/or modified at the at least one wheel, and/or after the braking torques and/or drive torques have been briefly generated and/or modified at the at least one wheel, the variable quantitatively describing the wheel behavior is determined for that at least one wheel, at least as a function of the variable describing the wheel rotation speed of that wheel. To detect the tilt tendency of the vehicle, during the time period in which the braking torques and/or drive torques are being briefly generated and/or modified at the at least one wheel, and/or after the braking torques and/or drive torques have been briefly generated and/or modified at the at least one wheel, the resulting change in the variable quantitatively describing the wheel behavior is determined. A tilt tendency of the vehicle about a vehicle axis oriented in the longitudinal direction of the vehicle exists if the magnitude of the resulting change in the variable quantitatively describing the wheel behavior is greater than a corresponding threshold value.
In this case, what is used as the variable quantitatively describing the wheel behavior is the variable that describes the slip. In other words, during the time period in which the braking torques and/or drive torques are being briefly generated and/or modified at the at least one wheel, and/or after the braking torques and/or drive torques have been briefly generated and/or modified at the at least one wheel, the variable that describes the change in the slip of the respective wheel is determined. Consequently, a tilt tendency of the vehicle exists if the magnitude of the variable that describes the change in the slip of the respective wheel is greater than a corresponding threshold.
Advantageously, a determination is made, at least as a function of one of the determined variables representing the transverse dynamics of the vehicle, as to which wheels of the vehicle are suitable for detecting a tilt tendency of the vehicle about a vehicle axis oriented in the longitudinal direction of the vehicle. Detection of the tilt tendency of the vehicle is advantageously accomplished on the basis of at least one of these wheels, by briefly generating and/or modifying braking torques and/or drive torques at at least one of those wheels. In particular, the wheels of the vehicle located on the inside of the curve are selected in this context.
According to a second recognition system, a tilt tendency for the vehicle exists if, for at least one wheel, the value of the variable quantitatively describing the wheel behavior is greater than a first threshold value; or if, for at least one wheel, the value of the variable quantitatively describing the wheel behavior is less than a second threshold value; and/or if, for at least one wheel, the magnitude of a difference that is constituted from the value of the variable quantitatively describing the wheel behavior and from a comparison value is greater than a corresponding threshold value; and/or if, for at least one wheel, the magnitude of a variable that describes the change over time in the variable quantitatively describing the wheel behavior is less than a corresponding threshold value; and/or if the magnitude of a variable describing the angle of inclination of a wheel axle is greater than a corresponding threshold value, the variables quantitatively describing the wheel behavior being determined for each of the wheels of the corresponding wheel axle, and the variable describing the angle of inclination of the wheel axle being determined as a function of those variables. Or a tilt tendency for the vehicle exists if the magnitude of a difference that is constituted from a variable describing the vehicle speed and from a speed limit value is less than a corresponding threshold value.
In this case, the variable that describes the diameter or the radius of a wheel is used as the variable quantitatively describing the wheel behavior.
It is particularly advantageous if stabilizing braking interventions are performed, at least on the front wheel of the vehicle on the outside of the curve, in such a way that a braking torque is generated and/or increased at that wheel. Advantageously, engine interventions and/or interventions on suspension actuators are also performed in order to stabilize the vehicle.
The apparatus according to the present invention for stabilizing a vehicle in the presence of a tilt tendency, with which a tipover of the vehicle is prevented, contains means with which, in the presence of a tilt tendency, at least stabilizing braking interventions are performed on at least one wheel of the vehicle. The apparatus further contains means with which, for at least one wheel, a variable that describes the change in the slip of the respective wheel is determined and with which, as a function of that variable, a determination is made as to whether a tilt tendency about a vehicle axis oriented in the longitudinal direction of the vehicle exists for the vehicle. Alternatively or additionally, the apparatus contains means with which a variable describing the diameter or the radius of the respective wheel is determined, and further means with which, as a function of the variable describing the diameter or the radius of the respective wheel, determines whether a tilt tendency about a vehicle axis oriented in the longitudinal direction of the vehicle exists for the vehicle.
A further advantage is the following: The result of the method according to the present invention is to stabilize a vehicle in the presence of a tilt tendency, i.e. the method prevents a tipover of the vehicle. For this purpose, a determination is made as to whether a tilt tendency about a vehicle axis oriented in the longitudinal direction of the vehicle exists for the vehicle. If a tilt tendency exists, a stabilizing braking intervention is performed in controlled fashion on the front wheel of the vehicle on the outside of the curve.
Performing the controlled braking intervention on the front wheel on the outside of the curve has the following advantage: The conventional methods only propose braking interventions such that a reduction in the vehicle speed is achieved. Since none of the wheels is braked in controlled fashion, with this type of braking intervention it is not possible to apply a controlled yaw torque to the vehicle. Since a vehicle behaves in a strong oversteering fashion before tipping over, by way of a controlled braking intervention and the application of a yaw torque, it is possible to achieve a stabilization of the vehicle that, for example, counteracts the oversteering of the vehicle.